Apparatus for controlling or assisting respiration



May 7, 1963 G. D. BLACK 3,088,455

APPARATUS FOR CONTROLLING OR ASSISTING RESPIRATION Filed Nov. 16, 1959 Inventor GEOFFREY DONALD BLAQIL 4 Attorney f United States Patent 3,088,455 APPARATUS FOR CO TROLLING 0R ASSISTING RESPIRATION Geoflrcy Donald Black, Tottenham, London, England, assignor to The British Oxygen Company Limited, a company of Great Britain Filed Nov. 16, 1959, Ser. No. 853,352 Claims priority, application Great Britain Nov. 19, 1958 5 (Ilaims. (Cl. 128-29) This invention relates to apparatus for controlling or assisting respiration.

In apparatus of the type adapted alternately to force gas or a mixture of gases into and to permit gases to be released from a patients lungs, it is well known to employ gas under pressure hereinafter termed pressurizing gas, to provide the motive force.

More particularly for resuscitation purposes the pressurising gas itself may be directed into the lungs, but if it is desired to conserve the exhaled gases for rebreathing, for example during the administration of anaesthetic gas mixtures, an expandable reservoir such as a flexible bellows or bag may be connected in the respiratory circuit, the reservoir being enclosed in a rigid airtight chamber, and the pressurising gas may then be delivered to the interior of the chamber to compress the reservoir during the inhalation phase. In a closed circuit system of this type, provision must be made for admitting oxygen to the system as it is consumed by the patient and for removing carbon dioxide.

Irrespective of whether the pressurising gas is supplied directly to the lungs or is used merely to compress a respiratory bag, it is desirable to provide timing mechanism by means of which the duration of the respiratory cycle may be controlled. It is also desirable to provide means for adjusting the positive trip pressure, that is the maximum pressure which it is desired to produce in the lungs during the inhalation phase and which causes the apparatus to switch from the inhalation phase to the ex halation phase of the respiratory cycle.

Heretofore it has been known to provide a pressure responsive member coupled to valve means for controlling the flow of pressurising gas, the pressure responsive member being subjected on one side to an adjustable loading force and on the other side, during the inhalation phase, to a pressure closely related to the pressure within the lungs. Provision is made for relieving the gas pressure on this side of the pressure responsive member during the exhalation phase. For example, the pressure may be relieved through an adjustable bleed in order that the duration of the exhalation phase may be made independent of the duration of the inhalation phase. At the end of the inhalation phase, that is, when the pressure within the lungs reaches the positive trip pressure, the valve means is moved by the pressure responsive member to cut off the flow of pressurising gas. When the gas pressure acting on the pressure responsive member is reduced to atmospheric pressure, that is at the end of the exhalation phase, the valve means is moved to restore the flow of pressurising gas. The coupling between the valve means and the pressure responsive member is preferably arranged to give a snap action to the valve means.

It will be appreciated that the duration of the exhalation phase is determined by the size of the bleed and by the magnitude of the loading force on the pressure responsive member. The disadvantage of this arrangement is that adjustment of the loading force on the pressure responsive member varies both the positive trip pressure and the duration of the exhalation phase. Although this could be compensated for by subsequently adjusting the size of the bleed, this procedure is inconvenient and some 3,088,455 Patented May 7, 1963 ice time may elapse before the correct setting is obtained to restore the exhalation phase to its original duration.

It is an object of the present invention to provide a combined pressure control and timing means for apparatus of the type specified which permits substantially independent adjustment of the positive trip pressure and the duration of the exhalation phase.

According to the present invention, in apparatus for controlling or assisting respiration of the type hereinbefore specified, a combined pressure control and timing means for interconnection between a source of pressurising gas and means for delivering gas under pressure to the lungs comprises a chamber having one wall formed as a pressure responsive member, valve means coupled to the pressure responsive member for controlling the flow of pres surising gas, inlet means for admitting gas at a pressure closely related to lung pressure to the interior of the chamber during the inhalation phase of the respiratory cycle, the pressure responsive member being movable in response to the production of a predetermined pressure in the lungs to close the valve outlet means, means for releasing gas at a controlled rate from the chamber during the exhalation phase of the respiratory cycle whereby the pressure responsive member is moved to open the valve means, and adjustable loading means opposing movement of the pressure responsive member in a direction to close the valve means comprising first biasing means effective over the whole range of said movement of the pressure responsive member, and second biasing means efiective only to oppose the final stages of said movement.

The first and second biasing means may be a pair of separately adjustable springs, preferably a low rate spring and a high rate spring respectively. Adjustment of the first spring is intended to be carried out on the initial assembly and thereafter left undisturbed. This spring determines the minimum trip pressure and also serves to maintain a substantially constant load on the pressure responsive member during both the inhalation and the exhalation phases, irrespective of the setting of the second spring, which serves essentially for adjustment of the positive trip pressure alone. Adjustment of the second spring does not materially affect the duration of the exhalation phase since it is effective only during the final stages of the inhalation phase and consequently only during the initial stages of the exhalation phase.

The pressure responsive member may be a bellows or a diaphragm or piston forming one wall of a gas chamber, the interior of the bellows communicating through a nonreturn valve either with the lungs or with a rigid chamber surrounding a rebreathing bag.

The interior of the bellows may be vented to atmosphere through a bleed opening which is preferably adjustable in size so that the duration of the exhalation phase which is determined by the time taken for the pressure within the bellows to return to atmospheric pressure, may be varied.

The invention will now be described by way of example with reference to the drawing which illustrates diagrammatically a pressure and timing control mechanism for an automatic respirator.

As shown, the device includes a source of fluid under pressure in the form of bottled gas connected to the control unit at the inlet thereof. After passing through the control, gas is directed through the outlet and suitable conduits to a respiratory mask disposed over the patients face. In the example as shown in the drawing, as the patient inhales, suitable quantities of gas are introduced to the mask from the control unit; and during the period when the patient exhales, the flow of gas from the control unit is stopped and the exhaled gas is directed through suitable conduits to the interior of the bellows 9.

The mechanism consists of a housing 1 divided by a partition 2 of non-magnetic material into a valve chamber 3 and a chamber 4. Gas under pressure is supplied to the valve chamber 3 through an inlet 5 and is discharged through an outlet 6 which may be connected to an injector for entraining a diluent gas, the gas mixture then being directed either into the patients lungs or used to compress a reservoir bag. A valve member 7 cooperating with a fixed annular valve seat 8 controls the flow of gas to the outlet 6.

Fixed at one end to a wall of the chamber 4 is a conventional flexible bellows 9 which has a connection 10, provided with a non-return valve 11. The connection 10 is connected into a gas supply line of a respiratory circuit. Depending on the type of circuit, the supply line may be attached to a facepiece or may lead to a rigid chamber surrounding an expandable reservoir for inhalant gas. The interior of the bellows is thus subjected during the inhalation phase to a pressure closely related to lung pressure. An adjustable orifice bleed 12 permits gas to escape from the interior of the bellows 9 to atmosphere.

A magnetic coupling provided between the valve member 7 and the bellows 9 consists of a magnet 13 secured to the free end of the bellows 9, and a magnet 14 mounted in the chamber 4 adjacent the partition '2, the magnets 13 and 14 cooperating respectively with armatures 15 and 16 carried one at each end of a lever 17 which is pivotally mounted at its mid-point about a stud 18 mounted in the valve chamber 3. The valve member 7 is secured to the end of the lever 17 which carries the armature 16.

At the beginning of the inhalation phase, when the bellows 9 is collapsed, the armature 16 is attracted to the fixed magnet 14 so as to hold the valve member 7 away from the valve seat 8. As the bellows is inflated through the connection 10, the magnet 13 approaches the armature 15 until, when a certain degree of inflation is reached, the attraction between them is sufficient to overcome the attraction between the fixed magnet 14 and the armature 16, and the lever 17 pivots about the stud 18 to close the valve member 7 against the seat 8 with a snap action. Similarly, in reverse, when the bellows returns to the collapsed state the valve snaps into the open position. By selecting magnets of the required relative strengths it is possible to ensure that the valve remains open until the bellows 9 is fully inflated and remains closed until it is fully collapsed.

Inflation of the bellows is opposed by an adjustable spring loading applied to one end of a plate 19 the other end of which is secured to the free end of the bellows. The plate 19 is pivoted adjacent its spring loaded end about a pin 20' mounted in the chamber 4. The spring loading consists of a low rate spring 21 which bears continuously on the one hand against the end of plate 19 and on the other hand against the wall of chamber 4, and a high rate spring 22 mounted coaxially within spring 21. The mounting for the spring 22 consists of a threaded sleeve 23 which is screwed into a threaded opening in chamber 4 and carries a tubular member 24 which extends coaxially into the spring 21, the sleeve 23 is retained by a locking nut 25. A cap 27 is retained by and has a sliding fit in the end of the tubular member 24. The spring 22 bears at one end against the cap 27 and an adjusting screw 26 which is screwed into the sleeve 23.

The sleeve 23 is screwed into the chamber 4 until the cap 27 is correctly located with respect to the end of the plate 19, that is, so that the spring 22 is arranged to bear against the plate only over a small proportion of its range of movement occuring when the bellows is inflated during the final stages of the inhalation phase and the initial stages of the exhalation phase. Adjustment of the screw 26 is thus adapted to vary the positive trip pressure but has substantially no efiect on the duration of the exhalation phrase, this being determined by the deflation rate of the bellows 9 which is controlled by the force exerted by spring 21 in conjunction with the stroke volume of the bellows and the area of the bleed 12. The spring 21 is preferably selected to give the required loading without adjustment, but if necessary the effective loading may be varied by inserting one or more shims between the spring and the wall of the chamber 4 during assembly.

I claim:

1. In apparatus for controlling or assisting respiration of the type hereinbefore specified, a combined pressure control for interconnection between a source of pressun'zing gas and means for delivering gas under pressure to the lungs of a patient, said control including pressure responsive timing means comprising a variable capacity gas chamber having one wall formed as a pressure responsive member, control valve means in said control movable between open and closed positions, said valve magnetically coupled to said pressure responsive member to move said control valve between open and closed positions in response to pressure variations to control the flow of pressurizing gas through said control, inlet means in said control interconnecting said padent and said variable capacity gas chamber for admitting fiuid at a pressure closely related to said patients lung pressure to the interior of the variable capacity gas chamber during the inhalation phase of the respiratory cycle, said pressure responsive member movable in response to a predetermined pressure in the lungs to move said valve to the closed position, outlet means for releasing gas at a controlled rate from the chamber during the exhalation phase of the respiratory cycle whereby the pressure responsive member is moved to open said control valve means, and adjustable loading means opposing movement of said pressure responsive member to close said control valve means comprising a first biasing means connected to said pressure responsive member operative to bias said member in one direction over the whole range of movement of said pressure responsive member, and second biasing means effective to oppose selected stages of said movement.

2. Apparatus according to claim 1 wherein said sec ond biasing means is adjustable independently of said first biasing means.

3. Apparatus according to claim 1 wherein the means for releasing gas from the chamber consists of a bleed, the area of which is adjustable to vary the duration of the exhalation phase.

4. Apparatus according to claim 1 wherein said first and second biasing meanscomprise a pair of separately adjustable springs.

5. Apparatus according to claim 4 wherein the springs are coaxially mounted.

References Cited in the file of this patent UNITED STATES PATENTS 2,598,525 Fox May 27, 1952 2,736,331 Seeler Feb. 28, 1956 2,870,763 Stanton Jan. 27, 1959 

1. IN APPARATUS FOR CONTROLLING OR ASSISTING RESPIRATION OF THE TYPE HEREINBEFORE SPECIFIED, A COMBINED PRESSURE CONTROL FOR INTERCONNECTION BETWEEN A SOURCE OF PRESSURIZING GAS AND MEANS FOR DELIVERING GAS UNDER PRESSURE TO THE LUNGS OF A PATIENT, SAID CONTROL INCLUDING PRESSURE RESPONSIVE TIMING MEANS COMPRISING A VARIABLE CAPACITY GAS CHAMBER HAVING ONE WALL FORMED AS A PRESSURE RESPONSIVE MEMBER, CONTROL VALVE MEANS IN SAID CONTROL MOVABLE BETWEEN OPEN AND CLOSED POSITIONS, SAID VALVE MAGNETICALLY COUPLED TO SAID PRESSURE RESPONSIVE MEMBER TO MOVE SAID CONTROL VALVE BETWEEN OPEN AND CLOSED POSITIONS IN RESPONSE TO PRESSURE VARIATIONS TO CONTROL THE FLOW OF PRESSURIZING GAS THROUGH SAID CONTROL, INLET MEANS IN SAID CONTROL INTERCONNECTING SAID PATIENT AND SAID VARIABLE CAPACITY GAS CHAMBER FOR ADMITTING FLUID AT A PRESSURE CLOSELY RELATED TO SAID PATIENT''S LUNG PRESSURE TO THE INTERIOR OF THE VARIABLE CAPACITY GAS CHAMBER DURING THE INHALATION PHASE OF THE RESPIRATORY CYCLE, SAID PRESSURE RESPONSIVE MEMBER MOVABLE IN RESPONSE TO A PREDETERMINED PRESSURE IN THE LUNGS TO MOVE SAID VALVE TO THE CLOSED POSITION, OUTLET MEANS FOR RELEASING GAS AT A CONTROLLED RATE FROM THE CHAMBER DURING THE EXHALATION PHASE OF THE RESPIRATORY CYCLE WHEREBY THE PRESSURE RESPONSIVE MEMBER IS MOVED TO OPEN SAID CONTROL VALVE MEANS, AND ADJUSTABLE LOADING MEANS OPPOSING MOVEMENT OF SAID PRESSURE RESPONSIVE MEMBER TO CLOSE SAID CONTROL VALVE MEANS COMPRISING A FIRST BIASING MEANS CONNECTED TO SAID PRESSURE RESPONSIVE MEMBER OPERATIVE TO BIAS SAID MEMBER IN ONE DIRECTION OVER THE WHOLE RANGE OF MOVEMENT OF SAID PRESSURE RESPONSIVE MEMBER, AND SAID SECOND BIASING MEANS EFFECTIVE TO OPPOSE SELECTED STAGES OF SAID MOVEMENT. 